This invention relates to a method for removing volatile fission products from irradiated fuel by first passing a hydrogen-containing inert gas by said fuel which is heated to an elevated temperature of at least 1000.degree. C. and then passing inert gas alone by said fuel which is at said elevated temperature.
One of the problems associated with the use of nuclear fuel in power production and particularly the reprocessing of irradiated nuclear fuel is the ability to handle and confine the gaseous fission products formed during reactor operations. It is anticipated that in order to satisfy the world's electrical needs as we approach the year 2000, there will be an increasing amount of irradiated fuel produced. Along with the increased volume of irradiated fuel, significant amounts of fission products such as tritium, krypton, xenon and iodine will be formed. Recovery of fission products in nuclear fuel reprocessing plants of conventional designs is not practical because of the relatively small amounts of such products in each ton of fuel. This is particularly true of the hydrogen isotope tritium, which has a half life of 12.26 years and is a ternary fission product produced in relatively small quantities of about 1/1000 of an oz. in each ton of fuel. Such tritium fission product, in the form of tritiated water, becomes intimately mixed with thousands of gallons of process water. It would be necessary to remove the tritium from the large volume of water by a technique such as isotopic separation before the water could be released as either liquid or vapor. It is desirable to develop a suitable alternative method for removal of volatile fission products from irradiated fuel prior to initiation of the reprocessing procedure.
One process for the removal of volatile fission products from irradiated fuel prior to reprocessing has been developed by Oak Ridge National Laboratories and is referred to as voloxidation. Voloxidation, described in Oak Ridge National Laboratories Report ORNL-TM-3723, is a process for oxidizing irradiated fuel in the presence of air or oxygen at a controlled temperature in order to form a very fine powder of U.sub.3 O.sub.8 and release the volatile fission products. This process is very temperature sensitive and it has been estimated that in a large commercial plant the reaction temperature would have to be maintained within a relatively narrow range, probably at about 480.degree. C., plus or minus 10.degree. C.
Another technique for removal of volatile fission products involves a pyrochemical process wherein the fuel cladding is melted or alloyed with another metal followed by a reduction step wherein the uranium and/or plutonium metal are produced by reduction in the presence of a molten salt. The fission gases are released during the decladding and reduction steps; however, one disadvantage of this technique is the addition of salts to the waste stream.
While the above designated processes provide for the removal of volatile fission products from irradiated fuel prior to reprocessing, they could present some difficulties in large-scale commercial operations due to the narrow temperature range required in one system and the salt addition to waste streams in the second system. Therefore, a method for releasing volatile fission products from irradiated fuel under commercially reasonable processing conditions and in a commercially reasonable time is desirable and could result in major process economies in reduction of costs for the reprocessing of nuclear fuels.